Carrier frequency system



Aus- 31, 1943. w. HAGEN 2,328,450

CARRIER FREQUENCY SYSTEM Filed Oct. 10, 1941 Fig] 7?; AB

La BA Tr2 AB BA 7f3 I g I I I I l I l f Kl K2 K3 K4, l

0 2 5 6 8 9 /l l2 KH:

Patented Aug. 31, 1943 CARRIER FREQUENCY SYSTEM Wolfgang Hagen, Berlin, Germany; vestedin the Alien Property Custodian Application October 10, 1941, Serial No. 414,415 In Germany March 28, 1940 3 Claims. (Cl. 179-15) This invention relates to carrier frequency systems of the kind in which two or more wave transmission channels are used.

In prior systems of this type wave filters are arranged to separate each channel from the other channel and also to separate each direction of conversation from the other direction. This entails a large expenditure in filters.

In arrangements as provided by the .inventio one intercommunication band is based on a carrier the lower side-band of which is used for one direction of conversation while the upper sideband is employed for the other direction. Further, as regards a second intercommunication band, one direction of conversation thereof is created by means of the upper side-band of Aa second carrier while for the second direction the lower side-band of a third carrier frequency or both side-bands thereof are used.

In the drawing, Fig. 1 illustrates a frequency distribution suitable for carrying out the invention. Fig. 2 graphically represents a lter arrangement for this frequency distribution, Fig. 3 is a circuit diagram in which such filter arrangement is included, Figs. 4 and 5 are graphs referred to in explaining the function of arrangements as provided by the invention.

In Fig. 2, the frequency condition of the several transmisison channels can be seen. Figs. 1 and 2 illustrate that one conversation, which may be designated as lower conversation, is transmitted with the aid of a carrier T1'1=5kHz, that is 5 kilocycles per second. As regards the directions of this conversation, direction BA thereof is transmitted by the lower side-band K1 while the other or opposite direction, namely AB, is transmitted by the upper side-band K2. 'I'he upper conversation is transmitted with the aid of the carrier frequencies Tr2=7.5kHz and Trz=l2.5kHz

In the direction AB of this conversation, the transmission is effected by the upper side-band Ka of the carrier T12 while in direction BA the transmission is by means of the lower side-band K4 or by both side-bands of the carrier Tra.

The frequency distribution so obtained results in an expenditure of wave filters which is less than has been the case heretofore. The channels Kz, IQ are both of the same direction. The filters TP1 and HP1, 8, Figs. 2 and 3, hence have to cut olf the cross-talk attenuation only. By transmitting in the same direction no appreciable level differences between .the two lchannels will occur. Also no filter need be arranged between the channels K3, K4 of the upper conversation since the incoming low frequency arriving at NF; and NF: is limited by 10W-pass filters TPZ and the carriers are suppressed by the modulating arrangement. 'I'he lower side-band of channel KS3 is suppressed by the separating filter HP1, 8 which is effective between the two conversations. The upper channel K4 may be employed for transmitting both side-bands. 'I'his will be of advantage as regards eillciency. The line attenuation increasing in accordance with higher frequencies requires an increased transmitting power to be employed and in its turn acts in a manner similar to a low-pass filter.

If, however, in the case of special lines still other carrier frequencies are to be transmitted simultaneously then the attenuation of these lines should not greatly increase with higher frequencies. In this case it is advantageous to cut off the upper side-band of Tra from the lower side-band K4 in order not to render the used frequency band wider than it must be. This expedient purposely renounces the greatest eiliciencey and may do so since .the transmitting power of one side-band, namely of K4, is quite sufllcient. A low-pass filter 'IP12.2kHz may be provided for this purpose.

Fig. 4 shows .the frequency distribution and the curve of line attenuation in the case of a simple two-Way intercommunication, while Fig. 5 illustrates a frequency distribution suitable in cases where additional carrier frequencies belonging to another system are to be transmitted over the same line.

The direction of transmission of the upper conversation includes a modulator M and is accommodated to the line. The call receiving apparatus R is connected by high ohmic resistances in a manner to avoid loss of transmitting energy. Otherwise such loss would occur since the receiving side is connected in parallel with the transmitting side.

In order to choose the directions of conversation a changeover switch S1, S2, S3 is provided. In the case of the lower conversation the filters HP5.3 and TP4.7 are switched over at contacts S2, Ss while in the case of the upper conversation the carrier frequencies Trz and Tra are interchanged at contacts S1. The switching-over operation is effected with respect to the upper and lower conversations at the same time and in such a manner that the channels located in the middle and which correspond to the reference numerals 2, 3 always operate in the same direction. The two terminal stations may hence be made similar to each other, and by means of switch S1, S2, Sa, they may be adjusted to suit frequency conditions.

A low frequency line NF may be connected to the outgoing line over a low pass filter.

What is claimed is:

1. A carrier frequency system comprising means to produce three diierent carriers, a transmission linemeans to produce from each carrier a lower side-band and an upperside-band,means fortransmitting one direction of a conversation over said line through the lower side-band of one of said carriers while transmitting the other direction thereof over said line by the upper side-band of the same carrier, and means for transmitting one direction of another conversation over sai-d line through the upper side-band of a second carrier while transmitting the other direction thereof over said line by at least the lower side-band of the third carrier.

2. A system as denned in claim 1 and which comprises terminal stations similar to each other, wave lters, means to interchange these lters and thereby to interchange the directions of the conversation transmitted with the aid of a lower carrier frequency, and means to interchange the carriers and thereby to interchange the directions of the conversation transmitted by an upper. carrier frequency.

3. A system as dened in claim 1 and which comprises a transmission channel of lower carrier frequency, a transmission channel of upper carrier frequency, and two transmission channels of carrier frequencies between the two said frequencies, these two channels being of the same direction while the two former channels are both of a direction which is the reverse of the latter direction.

WOLFGANG HAGEN.` 

